DWM Vapor Intrusion Guidance

The Division of Waste Management (DWM) has developed guidance for environmental professionals and internal staff to assist in the investigation and evaluation of vapor intrusion at contaminated sites.

This guidance is applicable anywhere a vapor intrusion investigation is warranted by a program in DWM, except for the Underground Storage Tanks (UST) Section. Please consult with the DWM program overseeing the investigation for vapor intrusion investigations at sites contaminated with petroleum constituents only. If petroleum constituents are comingled with volatile organic compounds at a site being managed by a DWM program, the DWM Vapor Intrusion Guidance document should be used.  

In addition to the DWM Vapor Intrusion Guidance, the division created frequently asked questions about Trichloroethylene (TCE) in indoor air. Read below for more information. 

Guidance Documents

Tab/Accordion Items

The DWM Vapor Intrusion Guidance document was developed using established guidance from the U.S. Environmental Protection Agency, the Interstate Technology and Regulatory Council (ITRC) and other states, modified for the purposes of DWM. The guidance document presents basic vapor intrusion investigation, sampling, evaluation and mitigation approaches. It is intended to complement the rules and policies of DWM's cleanup programs. Any user of the DWM Vapor Intrusion Guidance document should always work in coordination with the appropriate DWM program overseeing the investigation of the site.  

Note: The DWM Vapor Intrusion Guidance document is currently undergoing revision.  One of the changes includes the elimination of published residential and non-residential screening level tables that will be posted on this webpage. Updated (May 2020) Vapor Intrusion Screening Levels (VISLs) for groundwater, soil gas and indoor air are now accessible only by using the DEQ Risk Calculator. To provide for conservative screening, the residential and non-residential values provided represent the lower of the carcinogenic screening level at 1E10-6 cancer risk or the non-carcinogenic hazard quotient (HQ) of 0.2. If a screening level is exceeded and/or more than five compounds with a non-cancerous effect are present, the user is instructed to evaluate risk using the DEQ Risk Calculator. Please visit What’s New to the DEQ Risk Calculator (July 2020) for simple instructions on using the DEQ Risk Calculator to evaluate the vapor intrusion pathway. Note that it is NCDEQ policy to base mitigation decisions on risk to human health and not screening levels.

References in the existing March 2018 DWM Vapor Intrusion Guidance document to screening levels should now be applied using the VISLs obtained through use of the DEQ Risk Calculator.  The screening level references will be updated in the DWM Vapor Intrusion Guidance document in the current revision being completed.

Do not refer to or use any previously printed screening tables since they may not contain the most current toxicological data. Be sure to always access the DEQ Risk Calculator and other risk resources from the website to be sure you are using current versions.  

The state of science with regards to vapor intrusion is continually evolving; therefore, DWM will make updates to the guidance document as needed in order to continue to protect human health from exposures caused by subsurface vapor intrusion. The guidance document was prepared by DWM in cooperation with the DWM Remediation Team, a technical group comprised of representatives from all sections of DWM. Additionally, the guidance document was reviewed by several outside contractors and vapor intrusion professionals.

It is DWM's intent to place the guidance document in use and solicit any feedback for future revisions as it is being used. Please submit any feedback (via email only – no phone messages please) to Delonda Alexander, Superfund Special Remediation Branch Head at Delonda.Alexander@ncdenr.gov for future revisions. Any comments or questions regarding how to implement the guidance document should be discussed directly with the appropriate DWM program overseeing the site's activities.  

Following the Secretary’s Science Advisory Board’s (SAB) approval of Trichloroethylene (TCE) vapor intrusion action levels in February 2019, the division has prepared updated guidance and factsheets regarding the implementation of these action levels:

The supplemental guidance and the action levels were developed through extensive coordination with the North Carolina Division of Public Health (NCDPH) and with the EPA Region 4. The SAB’s review and endorsement process included the request for and consideration of public comment. Prior to the DEQ and the NCDPH submission of the Guidance and the Action Levels to the SAB in June of 2018, DEQ's staff made presentations and requested stakeholder comment on draft Guidance and Action Levels at the following venues:

  • North Carolina Manufacturer’s Alliance – September 2016
  • American Council of Engineering Companies and Professional Engineers of North Carolina – October 2016
  • Environmental Health Subcommittee of the North Carolina Association of Local Health Directors –February 2017
  • Registered Environmental Consultants update training by DEQ staff and REC Newsletter – March 2017
  • North Carolina Bar Association – Environment and Natural Resources Subcommittee Annual Meeting – May 2017
  • Dunklee and Dunham Vapor Intrusion Symposium – August 2017
  • Association of Engineering Geologists National Vapor Intrusion Symposium – October 2017
  • North Carolina Department of Labor staff – December 2017